Dear John,
Thank you very much for the explanation. It cleared up my confusion
about the syntax of "if ... else...", which in the help page of "if" said:
```
In particular, you should not have a newline between ‘}’ and
‘else’ to avoid a syntax error in entering a ‘if ... else’
construct at the keyboard or via ‘source’.
```
Best,
Jinsong
On 2022/10/21 21:49, John Fox wrote:
Dear Jinsong,
When you enter these code lines at the R command prompt, the
interpreter evaluates an expression when it's syntactically complete,
which occurs before it sees the else clause. The interpreter can't
read your mind and know that an else clause will be entered on the
next line. When the code lines are in a function, the function body is
enclosed in braces and so the interpreter sees the else clause.
As I believe was already pointed out, you can similarly use braces at
the command prompt to signal incompleteness of an expression, as in
> {if (FALSE) print(1)
+ else print(2)}
[1] 2
I hope this helps,
John
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